During the start-up of a glass fiberizing melter or furnace, it is necessary to operate the furnace for an extended period of time, on the order of 5 days, to flush out refractory residue from the construction of the furnace and to ensure stability of the heat pattern of the furnace and the composition of the glass being melted. During this period of time, molten glass must constantly flow from the furnace or "drain." Since the glass is not of commercial quality and the glass cannot be fiberized to form acceptable continuous fibers, the glass flows through a "drain bushing" rather than through a fiberizing bushing.
Such drain bushings, as conventionally utilized in the prior art, are formed of platinum or a platinum alloy, just as are the conventional fiberizing bushings. The conventional drain bushing is of concavo-convex interior configuration to define a glass receiving chamber having an open top surrounded by a peripheral flange which abuts against the lower surface of a conventional bushing block so that glass from the furnace or forehearth drains directly into and through the drain bushing. Glass exists from the drain bushing through a limited number of tips, typically 3, of large diameter. Glass drained through the drain bushing is collected as cullet for disposal or remelting, as desired.
The use of platinum or platinum alloy drain bushings has been standard in the art, but such use results in the necessary expense of the precious metal forming the bushing, the necessity of maintaining a precious metal inventory tied up in such drain bushings, and the expense of control of the precious metal inventory. Consequently, considerable direct and indirect cost savings would result from the development of a drain bushing construction of non-precious metal.